A conventionally known example of a sensor having a sensor element section and a heater section is a gas sensor which detects the concentration of a specific gas contained in exhaust gas, such as an oxygen sensor or a nitrogen oxide (NOx) sensor. These gas sensors include a sensor element section which is formed of a solid electrolyte body whose main component is zirconia, and a heater section which heats the sensor element section so as to bring it into an activated state. In order to bring the sensor element section into an activated state, a sensor temperature control apparatus controls the pulse energization of the heater section to thereby control the temperature of the sensor element section.
The sensor temperature control apparatus includes a switching device for on-off controlling the supply of electricity to the heater section, and feedback-controls the duty ratio of energization control pulses input to the switching device such that the sensor element section is heated to a target temperature.
Notably, switching devices used for the sensor temperature control apparatus are categorized into a high-side-type switching device which is interposed between a power supply (power supply potential) and the heater section, and a low-side-type switching device which is interposed between the heater section and a ground potential. For example, Patent Document 1 discloses a gas concentration detection apparatus which uses a gas concentration sensor and whose heater control circuit includes a high-side-type switching device (switch) (FIG. 10) or a low-side-type switching device (switch) (FIG. 11).